Calendar printing is one of the most cost effective ways that you can spend your hard earned marketing dollars promoting your business throughout the year.
You have many Image options for your callendar
For images, you can use images of your own products, services, family, pets, books you’ve authored and snippets there from or from articles you have published. There are many images you can download for no or little coast but they will not serve you as well as personalized images of that which you are looking to promote.
In any case you will want to be sure that your images are 300 DPI, dots per inch and if unsure, you will want to be using images that are several MB or larger and CMYK when you add to your print file and not RGB as many are on the internet. If still not sure, blow up to 400 percent and that view is a good approximation of how they will print. If the images you have chosen for printing calendars are fuzzy, or bit mapped (pointed square pixels are visible) than the image is of low quality and should not be used for your calendar printing.
article from : http://www.blog.books-printing.org/?p=712